The present invention relates to an X-ray computed tomography apparatus for picking up a tomographic image of an object to be examined, and more specifically to an X-ray computed tomography apparatus having a gantry including a rotation component capable of rotating at high speed.
A rotation component is provided for the gantry of an X-ray computed tomography apparatus (to be called "CT" hereinafter). The rotation component can be rotated continuously by 360.degree. or more with respect to the fixation component of the gantry. Recently, the rotation speed of the rotation component has been increased to such a high speed of 1 sec/rot or higher.
The rotation component has, for example, a disk-like shape, a drum shape, or the like.
The rotation base having the drum shape has a flat ring-shaped rotation base serving as a bottom surface, and a plurality of units such as an X-ray tube unit, X-ray detection unit and cooling unit (these are called "rotation component units") are mounted onto the rotation base via a bracket and fixation bolts.
In the operation for mounting the rotation component units, the operator pulls up the rotation component units and positions the bracket to the unit mount surface of the rotation base. Then, the bracket is fixed to the rotation base with fixation bolts. With this structure, the fixation bolts serve to support not only the weight of the rotation component units, but also the load created by the centrifugal force due to the rotation of the rotation base, which acts on the rotation component units.
In another conventional example of CT, the rotation base is so formed that the cross section thereof has an L-letter shape. The CT of this type is equipped with a frame for mounting units appropriate for the respective rotation component units, and thus rotation component units are mounted on the unit mount frame.
These conventional CTs entail the problems which may be caused by the connection structure between the rotation components and rotation component units, and the structures of the rotation components themselves.
(1) As the rotation component rotates, the load created by the centrifugal force acting on the rotation component unit, is concentrated onto the fixation bolts which fixes the rotation component unit onto the rotation base. For example, in case where the operator fails to tighten fixation bolts for mounting the rotation component unit to the rotation base, it is possible that those bolts which have not tightened come off, and the rotation component unit fly away while the rotation component is rotating. Especially, in the case where the rotation component rotates at high speed, the possibility that the above-described danger occurs is increased, and therefore a sufficient safety cannot be assured for patents or operators.
(2) The position of the center of gravity of each rotation component unit in the rotation axis direction of the rotation component becomes remote from the unit mounting surface of the rotation base. When the rotation component rotates at high speed, the rotation base is deformed such that the opening of the drum is expanded, due to the centrifugal force acting on each rotation component unit. Therefore, it becomes difficult to keep a necessary positioning accuracy of the X-ray transmitting path when the rotation component rotates at high speed. Further, if the rotation base is excessively deformed, it may be even broken, or the deformed base may cause an abnormality in the CT image.
(3) There are occasionally cases where the rotation component unit is removed from the rotation base due to accident or the like. While removing a fixation bolt which connects the rotation component unit to the rotation base, the rotation component unit must be supported from below, or it must be hung from above, or some measures must be taken in order for the rotation component unit to fall. Thus, the operability is very low, and further there can be a problem in terms of safety while removing the unit.
(4) The rotation and lock of the rotation component are performed by a drive mode by which the connection is made with a belt. In case where the belt is broken by damage or any reason, the rotation component cannot longer be locked to stop the rotation. Therefore, there should rise a danger of a possible accident, in which, for example, the operator or the like is accidentally entangled into the rotation component which cannot longer be locked.
There is a tendency that the size of the rotation component unit is increased, and its weight continuously rises. Therefore, an unbalanced section is created in the rotation component as a whole in terms of weight, and there are increasingly a great number of cases where an excessive load is applied at one time on the belt during the maintenance in which rotation component units are replaced. For example, as the maintenance of replacing an X-ray tube unit which has a short life is repeatedly carried out, an excessive load is applied, thus increasing the possibility of the danger that it is broken.